Exhaust moisture reduction by prototype heat exchanger

ABSTRACT

A winter environment military vehicle having means for removing moisture and other condensibles from the engine exhaust so that the gaseous combustion products eventually discharged into the cold atmosphere will contain insufficient condensibles to form a visible fog. Elimination of visible fog avoids the problem of enemy detection of the vehicle by observance of tell tale fog cloud rising into the atmosphere. Fog elimination may be accomplished by routing the products of combustion through an air-cooled heat exchanger which cools the combustion products and thereby condenses out the fog-producing components before they reach the vehicle tail pipe.

United States Patent [191 Tedrow Dec. 23, 1975 EXHAUST MOISTURE REDUCTION BY PROTOTYPE HEAT EXCHANGER [22] Filed: Dec. 4, 1973 [21] Appl. No.: 421,571

[52] US. Cl. 60/320; 60/309; 123/4131 [51] Int. Cl. F01N 3/02 [58] Field of Search 60/309, 320; 123/4131,

[56] I References Cited UNITED STATES PATENTS 1,651,827 12/1927 Mallory 123/4131 1,831,159 11/1931 Burrows. 60/309 1,987,604 l/l935 Corbett 60/309 2,310,767 2/1943 Dun 60/309 2,591,187 4/1952 Nelson 60/309 3,269,110 8/1966 Caddell 60/320 3,439,657 4/1969 Gratzmuller 123/4131 FOREIGN PATENTS OR APPLICATIONS 469,160 7/1937 United Kingdom 60/320 914,450 7/1954 Germany 60/320 Primary Examiner'Douglas Hart Attorney, Agent, or Firm-John E. McRae; Peter A. Taucher; Robert P. Gibson [57] ABSTRACT A winter environment military vehicle having means for removing moisture and other condensibles from the engine exhaust so that the gaseous combustion products eventually discharged into the cold atmosphere will contain insufficient condensibles to form a visible fog. Elimination of visible fog avoids the problem of enemy detection of the vehicle by observance of tell tale fog cloud rising into the atmosphere. Fog elimination may be accomplished by routing the products of combustion through an air-cooled. heat exchanger which cools the combustion products and thereby condenses out the fog-producing components before they reach the vehicle tail pipe.

1 Claim, 2 Drawing Figures e r god US. Patent Dec. 23, 1975 3,927,526

lFig-Z EXHAUST Mots Tune REDUCTIONJBY PROTOTYPE HEAT EXCHANGER BACKGROUND or THE INVENTION completely vaporized water and other, condensible" hydrocarbon vapors.- Under summer conditions such tor l8, and then through the fan into the engine com- .partment.

' spaced apart approximately thesame distance as the condensibles in the engine exhaust gases remain in the gaseous state and thuspose no problem with regard to informingthe enemy of the vehicle location. Under winter conditions the moisture, and the other condensi- .bles, condense almost instantaneously as theengine SUMMARY OF THE INVENTION The present invention proposes an engine exhaust A arrangement wherein the exhaust gases I are passed through a heat exchanger that is cooled by an enginedriven fan. As the gasespass through the hea't exchanger, water and other condensibles are condensed and removed from the gas stream. The gas exiting through the tail pipe contains a lowered condensibles concentration, insufficient to form a visible fog,

THE DRAWINGS FIG. 1 fragmentarily illustrates a vehicle having one embodiment of the invention incorporated therein.

, FIG. 2 is a frontal view of a heat exchanger used in the FIG. 1 vehicle.

With more particular reference to FIG. 1, there is fragmentarily shown a military truck having a front hood l'2 which serves to house an internal combustion engine 'l4. The engine drive shaft 16 may be operatively connected to the ground-engaging wheels (not s'h'owrilto propel the vehicle in the usual fashion.

The engine may be of the liquid-cooled type wherein a waterantifreeze coolant solution is circulated through coolan't' passages in the engine block. A conventional engine-driven water pump (not shown) circulates the coolant through the engine and through a radiator 18 that is cooled by an engine-driven fan 20 disposed within a shroud 22. Radiator 18 includes the usual headers 24 and 26 at its upper and lower ends, andthe conventional finned core '28 therebetwe'en. Disposeddirectly in front of radiator 18 is a multi- "tube heat exchanger '30 having an upper header 32, a lower header 34,- and a single row of eight heat transfer tubes 36 extending therebetween. Tubes 36 are provided with plate type heat transferfins 38 along their entirelength for enhancing transferofheat to the flowing air stre'aiif'. Endplates 40 ma be suitably located at corresponding side walls of the radiator. The aim is to ensure that the facearea of each of units 18 and 30 is entirely-exposed to the action of fan 20,- whereby each of-theheat transfer units 18 and 30 are made as efficient as possible under given operating conditions. Heat exchanger 30 is preferably located relatively close to radiator 18. to-promot'e airflow through the exchanger.

. Header 32 of heat'exchanger 30 is connected to the engine exhaust manifold-44 by means of a large diameter tube 46. Header 34 is connected to a conventional tail pipe .48'by means of a large diameter tube 50. Hot combustion gases flow from manifold 44 through tube 46 andinto :header 32. The hot gases are then separated into eight individual gas streams as they flow downwardly into tubes 36. The streams recombine in lower header Y34, and flow to the atmosphere through tube 50'and tail pipe 48.

As the hot gases flowdownwardly through heat transfer tubes 36 they are cooled from a relatively high temperature, e.g. 550F, to'a relatively low temperature, e. g. 50F. The cooling effect is achieved by reason of thescrubbing action of the fan air moving across the surfaces of fins 38. The .cooled exhaust gases enter header .34 along with condensed liquid droplets of -water and hydrocarbons. The droplets are for the most part retained in-header 34,. while the cooled gases pass into tube 50; A small opening, pipe, valve, etc, may be located at-the .lower surface of header 34, as at point -52, to discharge the condensed liquid. The small opening is sufficiently small so. that only an insignificant I quantity of gas passes therethrough. A liquid trap could be providedtoentirely'preclude gas flow through the liquiddischarge opening. 1

It is believed that header 34 probably acts somewhat tinthe nature of an.inertial droplet separator, since presumably the liquid-gas mixture coming out of each tube 36 is caused to undergo a directional change as it flowsinto andalong the header; the curvedsurface of .the header may impart a further component of spin to the mixture.-At any rate, tests show that the heat exchanger does in fact remove condensed liquid droplets -fromthe gas stream without the need for a separate liquid separator device. v

Preliminary tests have been'conducted to compare performance with and without the FIG. 2 heat exchanger. Two vehicles were employed, each being a 2% ton winter environment military truck powered with an .internal combustion engine developing 146 brake horsepower; .The experimental heat exchanger 30 included two headers 32 and 34, each formed of steel pipe having a diameterof. about 3 inches and a length of about 20 inches. Each of the'eight heat .transfer tubes 36 was formed out of a 1 inch diameter copper tube having alength of about l9 inches. 7 a

When .a' vehicle of the above described type, but without heat exchanger 30, was run in an atmosphere of about minus 10 F the exhaust from the tail pipe was a highly visible white cloud containing entrained moisture droplets; presumably the moisture in the exhaust gas stream was instantaneously condensed as it passed from the relatively hot tail pipe out into the relatively cold winter atmosphere. When a similar vehicle, equipped with the described heat exchanger, was run under the same conditions (at the same time) the exhaust was substantially cloudless. Measurements showed a temperature at inlet header 32 of about 550F, and a temperature at the outlet header 34 of about 150F. It is believed that complete elimination of visible fog could be achieved by increasing the effective surface area of the heat exchanger so that the outlet header temperature was reduced to approximately 50F. Such an increase in surface area might be realized by various expendients, such as by increasing the number of heat transfer tubes or by using two rows of tubes instead of one row as shown.

The illustrated heat exchanger is a single pass unit wherein the heat transfer tubes are arranged in parallel flow relation, not series flow. With such an arrangement the upper ends of each tube are at approximately the same temperature, e.g. 550F, and the lower ends of each tube 30 are at the same temperature, e.g. 50F. The tubes therefore thermally expand and contract equally during operation of the vehicle so as to simplify the task of avoiding thermal strain. The heat exchanger can be mounted by rigidly clamping one of headers 32 or 34 in a fixed location, and allowing the other header to float, thereby relieving thermal stresses set up in tubes 36. A floating arrangement of this type permits use of plate type fins 38 instead of the more costly spiral ribbon type that would be required if the tubes did not expand equally.

End plates can be attached to the heat exchanger, or not, as the particular vehicle design may require. As shown, each plate 40 is attached to the heat exchanger by means of two plate-like brackets 41 carried by the endmost tubes 36; the brackets may be locked to the tubes 36 by the same process that is used to lock the fins 38 onto the tubes. Thus,as under conventional practice, mandrels may be run through the tubes to expand the tubes against the fin collars, not shown; at the same time the tubes lockingly expand within the holes in brackets 41. Plates 40 can be loosely joined to brackets 41 to avoid thermal distortion effects, as by means of ear-slot connections 43.

The illustrated parallel flow arrangement of tubes 36 advantageously distributes or separates the gas flow into eight separate flows. The linear flow rate of the gas in each tube 36 is about one-eighth of the flow rate that would be achieved in a comparison series flow arrangement. The parallel flow arrangement may suffer as respects heat transfer coefficient due to a lesser scrubbing action on the tube inner surfaces. However the parallel flow arrangement is believed to offer a significant advantage as respects a lessened pressure drop. The parallel flow arrangement also is probably preferable because of easier collection of the condensate. In a series flow arrangement the condensibles would alternately condense and reboil in different sections of the tube, presenting the problem of moving the condensate along the tube length. There would be the additional problem of adding tube surface to make up for the relatively ineffective surface covered by the liquid.

Heat exchanger 30 could presumably be arranged with the inlet header at the bottom of the device so that the gases were caused to flow upwardly through tubes 36. However it is believed that upflowing gases might tend to re-entrain condensed liquid droplets in the outgoing stream. The illustrated downflow arrangement is therefore the presently preferred arrangement.

Heat exchanger 30 could presumably be arranged with tubes 36 extending horizontally. However the device would need to be oriented in a slightly typed condition to achieve the necessary drainage of the tubes. During turning of the vehicle on downslopes or inclines, the heat transfer tubes might temporarily be prevented from draining properly. Therefore it is preferred to orient the heat exchanger with the tubes arranged vertically. The vertical tube arrangement may theoretically suffer in that the horizontal fins form ledges for potential collection of dirt or debris. However, it is believed that the fins can be kept sufficiently clean by periodic maintenance.

Tubes 36 are preferably chosen small enough to provide a sufficient tube surface area per unit cross section, yet large enough to avoid undesirably large pressure drops. Using round tubes, a tube diameter of at least about 1 inch is preferred; other tube configurations should use a correspondingly large hydraulic radius. The tubes are preferably spaced apart about 1 inch to achieve satisfactory fin area and free space for low drag on the fan-induced airstream.

Heat exchanger 30 was conceived as a device to prevent visible fog at the tail pipe under winter conditions. It appears however that the device may offer some advantage in military and/or civilian vehicles as an air pollution control device for removing objectionable vapors from engine exhaust gases. U.S. Pat. No. 3,691,772 indicates that hydrocarbons can be removed by routing the exhaust gases through a condenser. It appears that applicants heat exchanger 30 could be used to condense out objectionable vapors such as unburned hydrocarbons and sulfuric acid from the exhaust stream. The liquid condensate might in some situations have to be collected in a holding tank connected to discharge opening 52.

U.S. Pat. No. 1,715,630 to S. A. Snell and U.S. Pat. No. 2,116,718 to P. T. Stubbs indicate that exhaust gases can be muffled by cooling processes. Apparently such cooling processes lower the density of the gases to produce a lessened pressure at the tail pipe, hence a lessened shock wave and lessened auditory output. The presumed operation supposedly follows the equation:

where subscript 1 refers to conditions upstream from the heat exchanger, and subscript 2 refers to conditions at the tail pipe discharge.

Since V substantially equals V the cooling of the gases from temperature t, to temperature results in a corresponding pressure drop from P to P and a correspondingly low pressure disturbance at the tail pipe discharge. It is believed that applicants heat exchanger 30 could produce a sound muffling action on the exhaust gases so as to avoid the need for the conventional muffler or to at least improve the sound muffling action when a conventional muffler is used.

I claim:

1. A land vehicle adapted for use in winter environments comprising a propulsion engine of the liquidcooled type; means for cooling the engine including a radiator for reducing the temperature of the coolant,

and a fan for drawing air through the radiator; duct means for exhausting combustion products from the engine; said exhaust duct means comprising a multitube heat exchanger located upstream from the radiator in near adjacency to the radiator and directly in the airstream developed by the fan, whereby both the radiator and heat exchanger are air-cooled by said fan; said heat exchanger having sufficient tube surface area so that the gases discharged to the winter atmosphere have insufficient condensibles to form a fog visible beyond sight of the vehicle; the radiator and heat exchanger occupying spaced vertical planes forward of so that each face area is entirely exposed to fan action. 

1. A land vehicle adapted for use in winter environments comprising a propulsion engine of the liquid-cooled type; means for cooling the engine including a radiator for reducing the temperature of the coolant, and a fan for drawing air through the radiator; duct means for exhausting combustion products from the engine; said exhaust duct means comprising a multi-tube heat exchanger located upstream from the radiator in near adjacency to the radiator and directly in the airstream developed by the fan, whereby both the radiator and heat exchanger are air-cooled by said fan; said heat exchanger having sufficient tube surface area so that the gases discharged to the winter atmosphere have insufficient condensibles to form a fog visible beyond sight of the vehicle; the radiator and heat exchanger occupying spaced vertical planes forward of the fan; the heat exchanger comprising an inlet header for receiving gases from the engine, an outlet header directly below the inlet header, and a number of heat transfer tubes extending vertically between the headers in the airstReam developed by the fan, said heat transfer tubes being arranged in parallel flow relation to receive component gas streams from the inlet header for individual cooling by the airstream; said heat exchanger and radiator having approximately the same face area so that each face area is entirely exposed to fan action. 